Magnetic resonance imaging (MRI) has been used successfully to study blood flow in vivo. Moreover Villringer et al., Magnetic Resonance in Medicine 6:164-174 (1988), Cacheris et al. Society of Magnetic Resonance in Medicine, 7th Annual Meeting, San Francisco, 1988 (SMRM 1988) Works in Progress, page 149 and Belliveau et al., SMRM 1988, Book of Abstracts, page 222 have proposed the use of certain paramagnetic lanthanide chelates as magnetic susceptibility, that is T.sub.2 * shortening, MRI contrast agents for studies of cerebral blood flow.
Unlike many previous imaging procedures, T.sub.2 or T.sub.2 *-weighted MRI using magnetic susceptibility (MS) contrast agents (hereinafter MS imaging) enabled blood perfusion deficits, e.g., cerebral ischemia, to be visualized rapidly as the MR signal intensity was reduced in the regions of normal perfusion due to the effect of the contrast agent, with ischemic tissue being revealed by its retention of signal intensity.
Blood perfusion deficits are associated with several serious and often life-threatening conditions. Rapid identification and localization of such deficits is highly desirable in order that the appropriate corrective action, be it therapeutic or surgical, may be taken promptly. Thus in the case of cerebral ischemia for example any delay in post-ischemic recirculation and reoxygenation of brain tissue reduces neuronal survivability.
MS imaging therefore represents a major improvement over routine T.sub.2 or T.sub.2 *-weighted imaging in the absence of MS contrast agents since in the routine procedures ischemia or infarcts only become detectable 2 to 3 hours after the event, e.g., a stroke, which gave rise to the perfusion deficit. However, while determination of the existence and location of a perfusion deficit is important, it is also desirable to be able to detect the degree or severity, and if possible the onset and duration, of blood flow abnormalities or variations in a quantifiable manner and we now propose that this be done using a modified MS imaging procedure.